Sound futures

Architects use computer software to construct three-dimensional models so
their clients can see how a finished building will look. Now some of them are
also creating computer models that simulate the acoustics so that clients can
find out how it is likely to sound.

The software assesses the shape of a room and the characteristics of its
surfaces, such as upholstered seating or bare plaster walls, and produces an
approximation of what listeners will hear in the space when people speak or make
music in it, long before the actual church hall or shopping centre atrium is
built.

Once such predictive programs were relative rarities, used mainly for the
planning of high-profile performance spaces. As computers have grown more
powerful and programs that once took a weekend to execute now take only hours on
a laptop, the simulation process, known as auralisation, is being used to plan
more commonplace locations such as airport concourses and video conference
rooms.

"Concert halls are the most critical listening spaces, but they are not the
only ones where sound is important," says Rendell Torres, an assistant
professor in architectural acoustics at New York's Rensselaer Polytechnic
Institute.

"There are lots of ways the acoustics of a room can help or hinder people in
what they are doing."

For example, Torres says bad acoustics in a building lobby can make a
receptionist's job difficult.

Experts in the field believe that auralisation technology can forestall
acoustic problems.

"When we created the simulation we heard a strong reflection from the second
and third tiers," he says.

Campbell soon realised that the sound was coming from a stone wall that had
been designed to be part of the space. Auralisation helped him not only to find
the problem, but to convince others that it existed.

"We handed people a set of headphones and they heard this terrific echo
bouncing off the wall," Campbell says.

The wall was soon redesigned.

Acoustics expert Dennis Paoletti, who heads the San Francisco office of
consulting firm Shen, Milsom and Wilke, agrees that auralisations are powerful
tools in demonstrating predicted acoustics to clients.

During one project designing a cathedral, for example, he and his colleagues
found that the reverberations - the time it takes for a sound to decay - would
last as long as 15 seconds rather than the desired interval of three to 3.5
seconds.

"We had the client listen to the auralisation," he says.

"There was no question then that we had a problem that needed to be
fixed."

Auralisation technology, however useful, is still far from perfect.

The programs generally do not handle the scattering of sound as well as they
model its reflection, according to Robert Coffeen, an associate professor of
architectural engineering at the University of Kansas.

"Any time you simulate acoustic conditions, you don't get the sound with
perfect accuracy," he says.

The software must be used carefully and needs to be backed up by
experience.

"Auralisation isn't there to tell us exactly 100 per cent how a room will
sound but to show changes in what it will be like as we change materials and
surface shapes within the hall," Coffeen says.

One problem is the scarcity of appropriate recordings for tests.

"The sound samples you are using have to be recorded in an anechoic chamber -
a room with no echoes," according to Lily Wang, a professor of architectural
engineering at the University of Nebraska.

But normal recordings are replete with reflected sounds.

To get around the problem, Wang says she and her colleagues hunted down and
shared anechoic samples.

She says recordings of individual voices or instruments are not that
difficult to locate, "but there just aren't that many samples of choruses".

So Ronald Freiheit, director of design engineering at the Wenger Corporation,
a maker of equipment for music education and performance in Minnesota, decided
to fill the gap by creating an anechoic choral recording. He believed such a
recording might help promote some of Wenger's acoustic products, including
orchestral shells designed to keep the sound of instruments or a chorus from
dissipating before it reached the audience.

"We wanted an auralisation to demonstrate the difference with and without the
enclosure," he says.

Wenger arranged to collaborate with 3M in St Paul, where 3M has a large
testing room lined with wedges of soft fibreglass to absorb sound. Freiheit also
lined up the St Olaf Cantorei, a singing group at St Olaf College in Minnesota,
to perform.

About 80 members of the choir and their conductor recorded a program in the
chamber standing on a grid above the fibreglass packing while singing, among
other works, a six-part mass and a motet by renaissance master Orlando
Gibbons.

Torres said the recording and similar projects would be useful as
auralisation grows more popular.

The choral music, for example, will be helpful to architects and clients
planning churches.

"It's really necessary to simulate what a space will sound like," he says.
"Otherwise it's like trying to describe a painting without actually showing it
to anyone."